The present invention generally relates to a braking circuit provided with an antilocking apparatus, and more particularly, prevents the pumping pulsation from transferring onto the master cylinder portion of a reflux system at the pumping operation time of the antilocking apparatus by discharging the operating liquid into the reflux passage from the wheel brake at the antilocking time to reflux it onto the master cylinder side by a pump provided in the reflux passage.
Conventionally, this type of reflux system of antilocking apparatus adopts a system of having
a) a reflux passage which is branched from a main flow passage for connecting a master cylinder with a wheel brake so as to return the operating liquid to a return point on the main flow passage on the upper stream side (namely, the master cylinder side) above the branch point,
b) a pump which is provided on the reflux passage to flow back the operating liquid,
c) a pressure governing means which is adapted to reduce the braking pressure of the wheel brake by the discharging of the operating liquid from the branch point into the reflux passage or to feed the operating liquid into the wheel brake by way of the branch point from the main flow passage of the downstream under the reflux point so as to increase the braking pressure of the wheel brake.
In the apparatus adopting the reflux system, a normally opened liquid pressure feeding valve by the electromagnetic operation on the main flow passage between the reflux point and the branch point is provided as, for example, the pressure governing means, and also, a normally closed liquid pressure discharging valve by the electromagnetic operation is provided on the reflux passage between the branch point and the pump so as to effect the brake liquid pressure control at the antilocking time through three modes of pressure reduction, retention, pressure increase by the switching operation of the two electromagnetic valves.
In the antilocking apparatus of the reflux system, the operating liquid to be discharged from the wheel brake is returned onto the master cylinder side by the pump at the antilocking pressure reduction time, so that the problems of noise and so on due to the vibrations of the brake pedal and the vibrations of the piping system by the pumping pulsation are caused.
In order to reduce the transferring of the pulsation of the pumping onto the master cylinder side, various methods are proposed. There are proposed, for example, a method (West Germany Patent Application No. 2643860) of providing a throttle between the pumping discharge opening and the return point, having a buffer chamber having the large area between the throttle and the pump discharge opening, and a method (Japanese Patent Publication Tokukohei No. 1-43663) of providing a check valve, between the return point and the master cylinder, with the side towards the return point from the master cylinder being in a forward direction, and also, a member slidably engaged with the check valve and a piston fixed to the member are provided, the volume of an accumulator portion for accommodating the operating liquid from the pump is increased by the movement of the slidable member, further the piston lowers the pumping discharge pressure so as not to transfer it onto the master cylinder side.
But there are various problems in the transfer preventing method of the pump pulsation conventionally proposed. Namely, the method of West Germany patent, there are problems that the load of the pumping becomes larger due to increase in the pump discharge pressure on the side of the throttle as the whole amount of the pump discharge amount passes through the throttle, and the size becomes larger due to the provision of the buffer chamber of the large diameter so as to require the end plug and so on. Also, the method of Japanese Patent Publication Tokukohei 1-43663 has problems in that the large accumulator portion is required, and as the size becomes larger, the cost become higher and so on, because the construction is extremely complicated, and all the pump discharge liquid is stored in amount in the normal antilocking condition so as not to return onto the master cylinder side under the normal antilocking condition.